Mapping the energy levels of an actinium molecule sought for symmetry-violation tests

Using relativistic coupled-cluster theory and a coupled-channel treatment of nuclear motion, this study maps the lowest rovibrational states of the actinium methoxide cation AcOCH₃⁺. The calculation captures anharmonicities and all rovibrational couplings to yield vibrational frequencies and state-specific electric dipole moments. Closely spaced doublets in symmetric-top molecules like this one amplify sensitivity to P- and T-violating interactions, making accurate spectroscopic predictions essential for designing future experiments. The results provide the spectroscopic benchmarks needed to assess the ion's suitability for laser cooling and precision symmetry tests.